PLANT CONSTITUENTS — CARBOHYDRATES 267 



called crude fiber. As there is always some mineral matter 

 present the actual determination is made by drying the cellulose 

 as above obtained and igniting it. The loss of dry material 

 on ignition is calculated as the actual crude fiber. (See below.) 

 As the method is wholly an empirical one, the crude fiber does 

 not represent pure cellulose, but is an approximation to it. 

 Probably the greater part of the crude fiber represents normal 

 celluloses, but with more or less unhydrolyzed hemi- and ligno- 

 celluloses. Part of these latter are, however, dissolved by the 

 treatment with acid and alkali. 



Cellulose Content of Crops. — The preceding table gives the 

 amounts of cellulose determined as crude fiber which are pres- 

 ent in the more important crops. 



EXPERIMENT STUDY XXXIII 



Cellulose in Plants 



Cotton. Examine cotton fiber and recall the study in Experiment 

 XXV. This is practically pure cellulose. (See analysis of cotton, 

 p. 263.) 



Crude Cellulose. Crude Fiber. Use 2.0 g. of ground hay or 

 grass. Place in a 500 c.c. flask and add 200 c.c. of 1.25 per cent hydro- 

 chloric acid, and boil with return condenser for one half hour. Filter 

 through a linen filter. Wash with hot water. Return the residue 

 to the flask and add 200 c.c. 1.25 per cent sodium hydroxide and boil 

 again with return condenser for one half hour. Filter through asbestos 

 and wash as before. The residue consists of the ash constituents plus 

 the crude cellulose. After drying, the loss of weight on ignition rep- 

 resents the crude cellulose, or, as it is termed, crude fiber. 



Starch 



The next carbohydrate to be considered is starchy with which 

 we may also group dextrin and inulin. While starch does not 

 occur as abundantly in plants as a whole as does cellulose, yet 

 it far outranks it in importance and value as a food. In fact, 

 starch is the most important carbohydrate food for both man 

 and animals. 



